Although a number of differing orthodontic techniques exist, the majority of orthodontists in practice in the United States, at the present time, utilize one of two basic techniques of orthodontic therapy in their treatment of patients. These basic techniques are the "light-wire" technique and the "edgewise" technique. Light-wire appliances were first designed and presented to the profession by an Australian orthodontist, R. P. Begg, who introduced the idea of differential force control. Since some types of tooth movements evoke more tissue resistance than others, and some movements occur faster than others, Begg reasoned that by selectively choosing the movements required and relating the reciprocal reactions properly, tooth movement might be accomplished in orderly manner. The Begg light-wire technique is characterized by a number of significant features. Brackets are fixed to all of the teeth of the patient anterior to and including the first molars. Archwires are round in cross-section and provide archform and leveling of the teeth. Archwires are loosely pinned to the bracket and are not ligated. The Begg brackets provide a single point contact with the archwire to minimize friction and permit the teeth to slide, rotate, tip and torque freely. Tip, torque and rotation are accomplished by auxiliaries and not by the active fit between the archwire and bracket as in the edgewise technique. Extra oral anchorage is not used. Reciprocal anchorage is provided for by selectively utilizing teeth posterior to extraction sites to retract teeth anterior to the extraction sites with intra and inter maxillary elastics. The light-wire appliances are now several and varied from the original design, although all employ sophisticated concepts in theories of tooth movement and anchorage control. Standard light-wire therapy does not utilize extra-oral traction, frequently involves extraction of teeth and typically employs more auxiliaries than conventional edgewise therapy.
The most widely utilized orthodontic therapy technique in this country, and the technique to which this invention is directed, is the "edgewise" technique, which was brought to the industry by Dr. Edward H. Angle. It should be understood, however, that this invention is also applicable to other orthodontic techniques such as the multi-phase and twin wire techniques, for example. In the beginning stages of edgewise therapy, archwires of circular cross-sectional configuration are employed. The greater flexibility of the round wire used in initial edgewise therapy permits greater range of movement of malposed teeth with less force to the teeth. For secondary and finishing therapy, the edgewise technique typically incorporates a multibanded precision appliance consisting of a labial archwire of rectangular cross-section configuration that is ordinarily of greater dimension at the sides than at the edges thereof. The archwire is fitted and ligated with metal ligature wire, or ligature elastics, or any other suitable form of mechanical retention, into precision mating horizontal archwire slots that are formed in brackets on all of the permanent teeth including first molars and frequently second molars. The archwire terminates in buccal tubes each having a rectangular passage through which the end portions of the rectangular archwire extend. The archwire, which may be composed of stainless steel or precious alloy, is typically positioned with its narrow dimension or edge lying against the labial and buccal surfaces of the teeth. This feature gives the technique its name "edgewise." The edgewise technique makes control possible in all directions and any individual tooth may be moved simultaneously in three directions; for example, an incisor may be moved lingually, distally and rotated around its long axis with one adjustment of the archwire. The rectangular cross-sectional configuration of the edgewise archwire permits it to be twisted to a desired extent and, being of spring-like nature, the twisting forces will be applied through the archwire to the teeth, thereby inducing a torquing movement of the teeth as the archwire becomes untwisted and returns to its normal configuration. The brackets are precision milled to define archwire slots of rectangular shape so that the orthodontist can select precision milled archwires to fit as precisely as desired. Tip, torque and rotation are accomplished by the fit between the archwire and the bracket. Extra oral anchorage may or may not be used as desired. Reciprocal anchorage can be provided by extraction of teeth and selectively utilizing teeth posterior to extraction sites to retract teeth anterior to the extraction sites with intra and inter maxillary elastics and/or closing loop archwires. This invention is generally directed to the edgewise technique as applied lingually to the teeth and concerns an orthodontic appliance system that integrates specific advantages that are afforded by edgewise appliances with both single and twin ligating tie wings.
As mentioned above, conventional edgewise therapy is typically accomplished by means of a labial archwire that is received by precision archwire slots formed by orthodontic brackets that are positioned at the labial surfaces of a patient's teeth. In many cases, undesirable psychological phenomena occurs since the appearance of a patient's teeth might be considered unpleasant, especially by the patient, because of the presence of orthodontic appliances on the labial and buccal surfaces of the teeth. Suppliers of orthodontic appliances, to provide for more aesthetically pleasing therapy, have in some cases eliminated the metal bands that typically encircle the teeth and have developed brackets that are adapted for direct bonding to the enamel surfaces of the teeth. Still, with the archwire present at the labial and buccal surfaces of the patient's teeth, it is not possible to provide the patient with an orthodontic appliance system that presents the teeth in their normal appearance. Further, by positioning orthodontic brackets on the labial and buccal surfaces of the patient's teeth, the orthodontic brackets frequently cause irritation of the lip and mouth tissues of the patient. Moreover, the mere presence of orthodontic brackets between the teeth and lips or cheeks can interfere to some extent with muscle tone and develop undesirable speech characteristics. In some cases, a patient's teeth may tend to decalcify or become permanently discolored in the area covered by or adjacent to metal bands. Also, in many cases, the orthodontic appliances interfere with efficient oral hygiene and caries can develop on tooth surfaces that cannot be properly cleaned. Consequently, when the appliances are removed from the patient's teeth, the otherwise pleasant appearance of properly occluding teeth can be marred by irregular surfaces, band lines of discoloration and fissures that can be developed in the enamel. By locating the appliances on the lingual surfaces of the patient's teeth, the labial surface will remain clear of obstructions that otherwise would interfere with efficient oral hygiene. It is desirable, therefore, to provide for lingual edgewise orthodontic therapy because of the effective nature thereof and to allow the labial surfaces of the teeth of the patient to remain unobstructed to permit efficient cleaning thereof and to provide the patient with a pleasant facial appearance during the period of orthodontic therapy. It is also desirable to provide lingual edgewise orthodontic therapy without subjecting the patient to the presence of brackets and archwires between the teeth and lip and cheek surfaces.
In some cases, it is desirable that the orthodontist be capable of applying tooth movement forces to the lingual surfaces of a patient's teeth. With conventional edgewise therapy, forces are typically applied through brackets that are positioned only at the labial and buccal surfaces. It is desirable, therefore, to provide orthodontic brackets that permit edgewise therapy through location of orthodontic brackets at the lingual surfaces of the patient's teeth.
Single tie wing type brackets for edgewise therapy typically incorporate a base structure which is formed to define a precision active archwire slot which receives the rectangular edgewise archwire therein. Single brackets also incorporate a pair of tie wings that extend from the base and are positioned on opposite sides of the precision archwire slot. These tie wings are typically centered with respect to the bracket structure and are therefore intended to be positioned in substantially centered mesio-distal relation with the facial surface of the tooth to which the bracket is secured. A ligature wire or elastic is looped over each of the tie wings and is passed over the archwire, thus securing the archwire firmly in its precision slot.
Single brackets provide maximum efficiency in the application of tipping and torquing movements to teeth but are minimally efficient in rotational control. Initially, rotational control was accomplished by soldering or welding eyelets at the extreme mesial or distal portion of the band attached to the tooth. The orthodontist could ligate the eyelet to the archwire, pulling that surface closer to the archwire and causing the tooth to rotate about the centrally located bracket. This is a cumbersome and inefficient method of rotational control.
Subsequently, fixed or flexible rotation levers, projecting mesially and distally, were added to the centrally located single bracket. Thus, a rotated tooth would have the rotation wing projecting more facially than the bracket. The archwire would touch the rotation wing and, as the wire is ligated into the bracket, cause the tooth to rotate about the bracket. The rotation lever is adjustable to project more or less to the facial as desired. This permits the orthodontist to select the amount of rotation desired by adjusting the rotation lever rather than adjusting the archwire.
The disadvantage of the rotation lever is evident in the initial stages of treatment. The archwire will not touch the rotation lever if a tooth is tipped and rotated severely and will prevent either action from occurring unless the archwire is adjusted to strike the rotation lever when ligated. Thus, initial archwire insertion can be inefficient and require more expertise to ligate.
Twin brackets were introduced to alleviate the inefficient rotation effectiveness of the single bracket. Instead of one centrally located bracket, two brackets were placed at the mesial and distal portions of the tooth. Thus, when each bracket is ligated to the archwire, the facial surface will align itself with the archwire, rotating the tooth.
One of the principles of rotation in orthodontics is over-correction of the original problem to compensate for the rebound or relapse tendency. This is especially indicated for rotated teeth. Twin brackets do not have the capacity to over-rotate within themselves. For over-rotation with twin brackets, the archwire has to be bent or some auxilliary must be added to force the mesial or distal portion of the bracket away from the archwire. Further, single edgewise brackets, without rotation levers, are also lacking in over-rotation control capability which will be discussed in more detail hereinbelow.
One of the more important advantages of single brackets is the advantage that is afforded by the active length of archwire existing between the points of connection to adjacent brackets. This active archwire length is known in the industry as "interbracket width". Since the connecting point between adjacent single brackets is established at substantially the center of the adjacent teeth, the archwire length, and thus the interbracket width, extends to points near the centers of adjacent teeth. The lengthy archwire span that exists between single brackets allows lower magnitude forces to be applied to the teeth over longer periods of time as compared to circumstances where the interbracket width is limited and the active archwire span is short. The long span of archwire may be twisted much further without causing permanent yielding or deformation of the metal of the archwire. Where the archwire between brackets is of limited length, which is typical where twin brackets are employed with the edgewise technique, application of large magnitude forces to the teeth can occur with only minimal twisting or other deformation of the archwire. Thus, after limited movement of the teeth occurs, the forces induced by the archwire dissipate quickly, thereby requiring frequent adjustment in order to maintain optimum force application. Of course, it is evident that frequent adjustment of orthodontic appliances necessitates frequent visits by the patient for adjustment of the orthodontic appliance and is therefore disadvantageous to the patient in this regard. Such frequent adjustment also requires a significant amount of chair time in the office of the orthodontist, thereby either increasing the cost of treatment to the patient, or minimizing the commercial advantage of orthodontic treatment on the part of the orthodontist. It is desirable, therefore, to provide a system for orthodontic treatment wherein patient visits are minimized and chair time is also minimized, to the mutual benefit of both the patient and orthodontist.
Twin brackets for the edgewise technique have been employed for a considerable period of time. Twin brackets typically incorporate a pair of spaced projections that extend from or are formed by the bracket base, each projection being formed to define a precision active archwire slot segment. The spaced active archwire slot segments cooperate to define a precision archwire slot having the effect of extending the entire length of the base. Each of the projections is provided with gingival and occlusal tie wings, the tie wings terminating at the opposed side portions of the base structure. With the base structure centered in respect to the tooth being moved, the tie wings will be positioned in pairs at opposite sides of the tooth, thereby defining bracket structure with rotational control. The orthodontist may utilize ligature wires or elastic members between selected tie wings and the archwire to develop the force moments that are necessary for efficient rotational control.
One of the typical disadvantages in utilization of twin brackets is the consequent minimization of interbracket width that exists as the result of positioning the tie wings at opposed side portions of the bracket structure. Ordinarily, as explained above, minimization of interbracket width, in conjunction with the edgewise therapy, suffers the disadvantage of requiring frequent patient visits and increasing chair time because of the necessity for frequent adjustment of the appliance in order to maintain the force levels within the optimum range for efficient tooth movement. It is desirable, therefore, to provide lingual edgewise therapy with twin brackets having the interbracket width of single brackets, thus combining the desirable features of both single brackets and twin brackets.
Another significant disadvantage in the utilization of twin brackets is that the spaces that are typically available between the tie wings of adjacent brackets leave insufficient room between the teeth for closing loops and tie-back loops. It is desirable, therefore, to provide a lingual orthodontic appliance system that affords the advantages offered by twin brackets and yet provides ample space between certain tie wings of adjacent brackets to facilitate efficient use of closing loops and tie-back loops in conjunction with edgewise orthodontic therapy.